There have been proposed a wide variety of function elements such as photoelectric conversion elements, thin-film transistor elements, light-emitting elements and the like, which utilize light-emitting properties or charge transport properties of organic materials. The organic materials of these elements are anticipated to bring about greatest advantages of organic materials such as lightweight, cheapness, lower production cost, flexibility, etc.
Of these function elements, various low molecular-mass materials or polymer materials have been proposed or reported for photoelectric conversion elements, particularly hole-transport materials of solar cells or electrophotographic photoconductors; typically, the former has been demanded for higher efficiency and the latter has been demanded for high-speed printing and durability.
As for materials of light-emitting elements, a wide variety of low molecular-mass or polymer materials have been reported. It is reported in the low molecular-mass materials that various laminate structures may achieve higher efficiency and suitably controlled doping processes may improve durability. However, it is also reported that, when the products are mass of low molecular-mass materials, films tend to change their conditions gradually with time; as such, there exists an essential problem in terms of film stability. On the other hand, polymer materials have been vigorously studied with respect to poly-p-phenylenevinylenes (PPVs) and polythiophenes in particular. However, these materials suffer from unsatisfactory purity and/or low fluorescence quantum yield in nature, thus high-quality light-emitting elements have not been currently achieved. In view of superior stability of polymer materials by virtue of their glassy state in nature, excellent light-emitting elements can be realized provided that polymer materials are allowed to take higher fluorescence quantum yield, thus further studies are being conducted under this concept. For example, polymer materials having a repeating unit of arylamine are the intended ones (see Patent Literatures 1 to 4 and Non-Patent Literature 1.)
In addition, the organic thin-film transistors using organic semiconductor materials have been actively studied and developed in recent years. The organic semiconductor materials can be easily formed into a thin film by an easy process such as a wet process, for example, printing, spin coating or the like. The thin-film transistors using organic semiconductor materials also have an advantage over thin-film transistors using inorganic semiconductor materials in that the temperature of the production process can be lowered.
Thus, a film can be deposited on a plastic substrate generally having a low thermal durability, so that electronic devices such as display devices can be reduced in weight and cost. Further, the electronic devices are expected to be widely used by taking advantage of flexibility of materials.
In addition, as for organic thin-film transistor elements, a wide variety of low molecular-mass or polymer materials have been reported. For example, as low molecular-mass materials, pentacene, phthalocyanine, fullerene, anthradithiophene, thiophene oligomers and bisdithienothiophene have been studied (see Patent Literature 6).
An organic thin-film transistor using pentacene as an organic semiconductor layer can have a relatively high field effect mobility. However, acene based materials have an extremely low solubility in a general solvent. Therefore, when such an acene based material is used to form a thin organic semiconductor layer of an organic thin-film transistor, a vacuum deposition process is necessary to be performed.
That is, the thin film cannot be deposited by an easy process, such as coating, printing or the like, and the acene based material does not always satisfy the expectation on the organic semiconductor material.
In addition, as polymer organic semiconductor materials, Patent Literature 2 and Patent Literature 3 respectively propose poly(3-alkylthiophen) and a copolymer of dialkylfluorene and bithiophene.
Since these polymer organic semiconductor materials have low but sufficient solubility by introducing of alkyl groups, a thin layer thereof can be formed by coating or printing without performing a vacuum deposition process.
These polymer organic semiconductor materials have high field effect mobility in a state in which molecules align. However, the alignment state of the molecules may be adversely affected by the kind of solvent and coating method during film deposition, resulting in a problem of variation of the transistor characteristics and poor quality stability.
Polymer materials such as polythiophene, polythienylenevinylene and polymers containing arylamine as a repeating unit have been also studied (Patent Literature 5).
Patent Literature 5 has been proposed by the inventors of the present invention. Although the polymer materials including the polymer materials having an arylamine unit, which are described in the related art, have remarkably enhanced their field effect mobility that is a specific property of organic electronic materials, materials having still higher field effect mobility are required in view of application to organic electronics, particularly organic FET elements.
In addition, the polymer materials are necessary to be sufficiently soluble into organic solvents in order to introduce into electronic elements greatest advantages of the organic materials, such as inexpensive production cost, sufficient flexibility and strength, lightweight, and possibility of having larger area. Pi-conjugated polymers, having a structure of stretched conjugate, typically often exhibit a rigid structure, causing lower solubility in general. The polymer materials in the related art described above are mostly difficult to be dissolved, thus various molecular designs have been tried so as to avoid the insolubility.    Patent Literature 1: U.S. Pat. No. 5,777,070    Patent Literature 2: Japanese Patent Application Laid-Open (JP-A) No. 10-310635    Patent Literature 3: JP-A No. 08-157575    Patent Literature 4: JP-A No. 2002-515078    Patent Literature 5: JP-A No. 2005-240001    Patent Literature 6: JP-A No. 5-55568    Non-Patent Literature 1: Synth. Met., 84, 269 (1997)    Non-Patent Literature 2: Appl. Phys. Lett., 69(26), 4108 (1996)    Non-Patent Literature 3: Science, 290, 2123 (2000)